Complete Nitrification Research Articles

Optimizing nitrogen removal in a hybrid oxidation ditch

Wastewater treatment plants are now facing the challenges of high cost, high energy consumption, while effluent quality is relatively poor with total nitrogen concentration exceeding the requirement of reuse. This study investigated the performance of contaminants removal, especially nitrogen by a hybrid oxidation ditch (H-OD) which is based on the theory of integrated fixed-film activated sludge under different control factors. The aeration rate, return ratio and hydraulic loading were controlled at 0.4 m3/h, 100% and 0.55 m3/m3 h, respectively as the optimized control parameter values. Under the optimized conditions, the effluent concentrations of chemical oxygen demand and ammonium were 35.8 mg/L, 1.04 mg/L, respectively, while the suspended solid was below 10 mg/L. The average removal rate of total nitrogen was 72.8%, and simultaneous nitrification and denitrification (SND) was achieved at 42.7%. Besides, when the carbon/nitogen ratio was maintained from 2.12 to 5.56, the complete nitrification and denitrification was obtained. The results showed that the H-OD was suitable for nitrogen removal and SND was very attractive for practical engineering applications.

Nitrite build-up effect on nitrous oxide emissions in a laboratory-scale anaerobic/aerobic/anoxic/aerobic sequencing batch reactor

Biological wastewater treatment processes with biological nitrogen removal are potential sources of nitrous oxide (N2O) emissions. It is important to expand knowledge on the controlling factors associated with N2O production, in order to propose emission mitigation strategies. This study therefore sought to identify the parameters that favor nitrite (NO2-) accumulation and its influence on N2O production and emission in an anaerobic/aerobic/anoxic/aerobic sequencing batch reactor with biological nitrogen removal. Even with controlled dissolved oxygen concentrations and oxidation reduction potential, the first aerobic phase promoted only partial nitrification, resulting in NO2- build-up (ranging from 29 to 57%) and consequent N2O generation. The NO2- was not fully consumed in the subsequent anoxic phase, leading to even greater N2O production through partial denitrification. A direct relationship was observed between NO2- accumulation in these phases and N2O production. In the first aerobic phase, the N2O/NO2- ratio varied between 0.5 to 8.5%, while in the anoxic one values ranged between 8.3 and 22.7%. Higher N2O production was therefore noted during the anoxic phase compared to the first aerobic phase. As a result, the highest N2O fluxes occurred in the second aerobic phase, ranging from 706 to 2416 mg N m-2 h-1, as soon as aeration was triggered. Complete nitrification and denitrification promotion in this system was proven to be the key factor to avoid NO2- build-up and, consequently, N2O emissions.

Dominance of comammox Nitrospira in soil nitrification.

The first and limiting step of nitrification is catalyzed by ammonia-oxidizing archaea (AOA) and bacteria (AOB). Recently, complete ammonia oxidizers (comammox Nitrospira) have been discovered to perform complete nitrification in one cell, yet their role in soil nitrification is still unclear. This study investigated the abundance and contribution of aerobic ammonia oxidizers in typical soil habitats, and assessed the role of comammox Nitrospira in ammonia-oxidizing communities. The results showed that comammox Nitrospira were dominant in 70% of the samples and their abundance displayed a significant positive correlation with nitrification potential. The median amoA gene transcription level of comammox Nitrospira exceeded that of AOA and AOB in in-situ soils. The abundance of comammox Nitrospira was negatively correlated with soil pH, dominating in 84% of soil samples with pH<6.17. The results challenge the role of AOA and AOB in soils, highlighting the importance of comammox Nitrospira in soil nitrification, especially in acid soils. This work supports better understanding and regulation of the soil nitrogen cycle.

Recovery of biological wastewater treatment system inhibited by oxytetracycline: Rebound of functional bacterial population and the impact of adsorbed oxytetracycline on antibiotic resistance

This study revealed the recovery process of an anaerobic–aerobic wastewater treatment system, which was seriously inhibited by oxytetracycline at 200 mg/L, over a period of 91 days after the antibiotic potency in the wastewater was removed through enhanced hydrolysis pretreatment (85 ℃ for 6 h). The organic loading rate (OLR) of the upflow anaerobic sludge bed (UASB) reactor was maintained at 2 g COD/L/d for 36 days in the first recovery stage, and gradually increased to 10 g COD/L/d in 4 steps. The UASB reactor fully restored its soluble chemical oxygen demand (SCOD) removal performance in the first stage, which was accompanied by the rebound of the hydrolysis/fermentation/acetogenesis bacteria, including vadinHA17_norank, Mesotoga, Longilinea, Anaerolineaceae_norank, Lentimicrobiu, Blvii28_wastewater-sludge_group, and Synergistaceae_norank. In the aerobic reactor receiving the effluent from the UASB reactor, stable SCOD removal occurred on day 54 and complete nitrification occurred on day 64 at an OLR and ammonia load of 0.147 g COD/L/d and 0.015 g N/L/d, respectively. The resistome abundances in the UASB and aerobic reactors decreased from 1.01 (copies/16S rRNA gene) and 1.11 to 2.7 × 10−1 and 3.0 × 10−1, respectively, over the whole experimental period. The relatively high resistome levels in the final stage might be associated with the adsorbed oxytetracycline in both reactors (7.4 ± 0.3 g/Kg and 0.7 ± 0.2 g/Kg, respectively). The result demonstrated that, for the biological systems damaged by high concentrations of antibiotics, their wastewater treatment functions could be recovered easily by removing influent antibiotics, but the further reduction of resistant determinants depended on the removal of adsorbed antibiotics.

Nitrification characteristics of long-term idle aerobic activated sludge during domestication.

Nitrite accumulation usually occurred when domesticating the idle aerobic activated sludge. A sequencing batch reactor (SBR) was used to investigate whether the short-cut nitrification sludge could be cultivated using the idle sludge as inoculated sludge. The results showed that the nitrification process consisted of three stages. In the first stage, the activity of ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) were very low with almost no nitrification performance. In the second stage, the activity of AOB started to recover with the effluent NH4+-N gradually decreased to 0.29mgL-1, while NOB was alternately inhibited by free ammonia (FA), free nitrous acid (FNA), and nitrite. The effluent NOx--N was mainly NO2--N with an average nitrite accumulation ratio of 74.00%. In the third stage, the nitrification altered from short-cut nitrification to complete nitrification, and the nitrification kinetics of AOB and NOB were both well-fitted to the Monod equation (R2 > 0.92). The variations of effluent pH and ORP between cycles could indicate the recovery stage of the nitrifying ability. Through monitoring the curves of effluent pH and ORP, when the domestication process is between the pH peak and ORP plateau, the short-cut nitrification sludge could be cultivated. This study revealed the mechanism of nitrite accumulation during the domestication of long-term idle aerobic activated sludge, and established a control strategy to accelerate the domestication.

Comparative Study between Membrane Bioreactor MBR and Rotating Biological Contactors RBC for Greywater Treatment

Greywater is the major part of water consumption in houses. Greywater should be treated to complying with the specifications for several purposes such as toilet flush, landscaping irrigation, and agriculture. The treatment efficiency of both MBR and RBC systems was investigated by using a verified mathematical model. The simulation program GPS-X (version 6.0) was used to simulate both MBR and RBC systems. The simulation model for biological treatment for both MBR and RBC systems is based on Activated Sludge Model 1 (ASM1). The experimental data for model calibration and verification for the MBR system were taken from experimental work done at Tubitak, Marmara Research Center, Turkey ATASOY. As well as the RBC proposed model was verified also by using RBC experimental results for a pilot plant according to BABAN. The RBC pilot plant consists of three units, The first is the RBC unit, the second unit is the settling tank and the last unit is the disinfection tank. The results of the MBR plant showed that the removal efficiencies of the greywater were: 95% for COD; 95% for BOD5; 96% for TKN; 92% for NH4+ and 99% for TSS. Whereas, the results of the RBC show that, The BOD efficiency removal was ranged between about 93.0 to 96.0 %, and for the total SS removal was ranged between 84.0 to 95.0 %. The MBR system provides complete nitrification and suspended solid removal. The RBC system provides less nitrification process and suspended solid removal. The effluent of the rotating biological contactors units for the greywater could be reused after filtration and disinfection with minimal cost of operation. The effluent of the membrane bioreactor unit needs only disinfection before reuse.

Effect of Different Parameters of The Biological Processes on The Specific Growth Rate of Nitrifying Bacteria by Means of Mathematical Models

In this study, the biological removal of nitrogen from wastewater with relatively high ammonium concentration is investigated by modelling and simulation. Specifically, the nitrification process, means the oxidation of ammonium to nitrate, which is catalysed by two types of bacteria, namely ammonium-oxidising bacteria (AOB) and nitrite-oxidising bacteria (NOB). In wastewater treatment, ammonia oxidation lowers the pH of wastewaters with in relation to total ammonia limited alkalinity. By reducing the pH, ammonia oxidation often stops just below pH 6-6.5. On the other hand, nitrification has been found to occur even at low pH in reactors that process human urine, although it was not clear which species of bacteria are involved. Against this background, this research used different mathematical models of ammonia-oxidising bacteria (AOB). The aim is to estimate those sludge residence times as a function of pH that can achieve complete nitrification of the NH3-N load in the influent. Quantity of base that should be dosed to the system and the capacity of the bioreactor have been calculated using estimated data. The values obtained have also been compared with the values from literature.

Impact of fertilization with pig slurry on the isotopic composition of nitrate retained in soil and leached to groundwater in agricultural areas

The isotopic composition of N and O of nitrate (NO3−) is usually employed to trace its sources of pollution in groundwater. In agricultural areas, the amount of NO3− that reaches the aquifers after fertilization is controlled by different transformation processes that can affect the nitrogen species isotopic composition. Aiming to address the reliability of using isotope tools to trace sources of groundwater NO3−, the goal of this study was to check the effect of fertilization on the isotopic composition of N compounds retained and leached from soils. The concentration and isotopic composition (δ15N and δ18O) of ammonium (NH4+), NO3− and nitrite (NO2−) was characterized after the application of pig slurry in lysimeters containing either soil under fallow (LF) or the same soil continuously cropped and fertilized (LC) during the previous six years. Results showed that the leached NO3− isotopic signature did not directly reflect the isotopic composition of the applied pig slurry. Just after fertilization, nitrification led to lower δ15NNO3 values in soil extracts and leachates (e.g. from +5.9 ± 0.9‰ to +3.8 ± 3.1‰ in soil extracts of LF lysimeters). These values increased after complete nitrification (+11.5 ± 1.3‰) towards the δ15Nbulk of pig slurry (+19.6 ± 0.5‰). Later on, due to soil organic matter and plant debris mineralization and subsequent nitrification, values decreased towards the initial δ15NNO3 of soil but remained above them (+8.6 ± 1.0‰). Both LF and LC experiments showed a similar trend and the latter ones allowed to reinforce that long-term fertilization with pig slurry can increase the soil δ15NNO3. Concerning the δ18O of NO3− from soil extracts and leachates, it mainly depended on the δ18O of irrigation water and oxygen, after nitrification of NH4+ from pig slurry. Therefore, studies aiming to trace groundwater NO3− pollution sources in rural areas by using an isotopic approach should consider the fertilization history of each setting. Also, analyzing the δ15Nbulk of soil is recommended, since it could mask the isotopic signature of the N applied through fertilization.

Enrichment and physiological characterization of a novel comammox Nitrospira indicates ammonium inhibition of complete nitrification

The recent discovery of bacteria within the genus Nitrospira capable of complete ammonia oxidation (comammox) demonstrated that the sequential oxidation of ammonia to nitrate via nitrite can also be performed within a single bacterial cell. Although comammox Nitrospira exhibit a wide distribution in natural and engineered ecosystems, information on their physiological properties is scarce due to the limited number of cultured representatives. Additionally, most available genomic information is derived from metagenomic sequencing and high-quality genomes of Nitrospira in general are limited. In this study, we obtained a high (90%) enrichment of a novel comammox species, tentatively named “Candidatus Nitrospira kreftii”, and performed a detailed genomic and physiological characterization. The complete genome of “Ca. N. kreftii” allowed reconstruction of its basic metabolic traits. Similar to Nitrospira inopinata, the enrichment culture exhibited a very high ammonia affinity (Km(app)_NH3 ≈ 0.040 ± 0.01 µM), but a higher nitrite affinity (Km(app)_NO2- = 12.5 ± 4.0 µM), indicating an adaptation to highly oligotrophic environments. Furthermore, we observed partial inhibition of ammonia oxidation at ammonium concentrations as low as 25 µM. This inhibition of “Ca. N. kreftii” indicates that differences in ammonium tolerance rather than affinity could potentially be a niche determining factor for different comammox Nitrospira.

Long-term Stability of Aerobic Granular Sludge Under Low Carbon to Nitrogen Ratio

Long-term stability is important for the practical application of aerobic granular sludge system under low carbon to nitrogen ratio (C/N). In this study, aerobic granular sludge, seeded in the reactors A and B, were cultivated under low C/N to investigate the properties, performance, and resilience to shock load in the long-term operation. The load of carbon and nitrogen in the feed was increased gradually. The C/N of reactor A was kept at 2, while that of reactor B was kept at 4 initially and then reduced to 2 in the shock load stage. It was discovered that the aerobic granular sludge stored at 4℃ for 30 days was essentially revived after 25 days of cultivation in reactors A and B, with over 90% removal efficiency for COD and ammonia, respectively. In the following stages, the removal efficiencies of COD and ammonia in reactor B were over 90% and complete nitrification was achieved. In contrast, in reactor A, the removal efficiency of COD was only 80% and only partial nitrification was achieved; however, ammonia removal efficiency of 90% was finally achieved. In the shock load stage, the COD removal efficiencies in reactors A and B were still above 80%, but the ammonia removal efficiencies were severely affected. The removal of ammonia was deteriorated in reactor A, while only partial nitrification was achieved in reactor B. During the entire operation, the physical properties of the aerobic granules in reactors A and B were barely affected, with sludge volume index (SVI30) in reactors A and B maintained at 60 mL ·g-1 and 75 mL ·g-1, and mixed liquid suspended solid (MLSS) at 5 g ·L-1and 3.7 g ·L-1, respectively. Microbial analysis showed that the aerobic granular sludge in reactor B has richer and more diverse microbial community than that in reactor A. The abundance of Zoogloea in reactor B, which is simultaneously able to produce polymeric protein and stabilize the structure of the aerobic granules, may be favorable for the high stability of the aerobic granules. These findings suggested that the aerobic granular system under the C/N of 4 had better performance in ammonia removal and higher tolerance to shock load, which guaranteed high stability of the aerobic granular sludge system in long-term operation, as compared to that under the C/N of 2.

The role of hydroxylamine in promoting conversion from complete nitrification to partial nitrification: NO toxicity inhibition and its characteristics

This study investigated a strategy for hydroxylamine (NH2OH) addition for promoting the conversion of complete nitrification to partial nitrification in a sequencing batch reactor (SBR). The results showed that continuous dosing of 5 mg-N/L NH2OH into a complete nitrification reactor for 16 days led to an increase in the nitrite accumulation ratio (NAR) from 0.22% to 95.08% and a significant enhancement in the accumulation of NO and N2O in the liquid. The maximum concentration of NO in each cycle rose with the increase of NAR during NH2OH addition. With the stopping of NH2OH addition, the partial nitrification disappeared progressively in 21 days. The analysis for microbial community showed that Nitrospira was the main NOB and its relative abundance decreased with NH2OH addition and recovered after the cessation of NH2OH addition. Accordingly, NH2OH has a significant and reversible inhibition on Nitrospira and its essence might be related to NO toxicity.

Analysis of municipal sewage pollution and denitrification treatment under low oxygen conditions

Anaerobic–Anoxic–Oxic (AAO) process is widely used in municipal wastewater treatment plants because of its simple structure, rich experience in engineering design, easy operation control and simultaneous nitrogen and phosphorus removal. The energy consumed in the aeration process occupies more than 50% of the total energy consumption of the sewage treatment plant, and reducing aeration is one of the major ways to reduce energy consumption. With the nitrification effect, the sewage treatment equipment controlled the dissolved oxygen (do) concentration in the aeration tank to 2 mg/L or more. The result shows that even nitrification can achieve complete nitrification. In a low oxygen state, the sewage treatment plant is reduced in energy consumption The degradation of pollutants in AAO process under different DO concentration was studied in a pilot-scale test. At the same time, the effects of temperature and carbon source on nitrogen removal in the system at low DO concentration were investigated, and the microflora structure was analyzed, in order to provide a reliable theoretical basis for the actual wastewater treatment plant to achieve stable and efficient nitrification at low DO concentration and save energy consumption. • Complete nitration can be achieved at a lower concentration of dissolved oxygen. • The influencing factors of pollutant degradation were analyzed. • The microflora structure was analyzed. • The influencing factors of nitrogen removal in the system were analyzed.

Microbial community and function evaluation in the start-up period of bioaugmented SBR fed with aniline wastewater

An enhanced sequencing batch reactor (SBR) system was developed to treat synthetic wastewater rich in 600 mg/L aniline. The aniline degradation efficiency was almost 100%, and the total nitrogen (TN) removal rate was more than 50%. Metagenomics technology revealed the community structure, functional genes and metabolic mechanism during the start-up of the enhanced reactor. Sequencing results showed that Proteobacteria, Bacteroidetes, Chloroflexi and Actinobacteria were dominant phylum. The proportion of degradation of aromatic compounds function increased gradually, but the proportion of nitrogen metabolism function changed little. Functional genes involved in aniline degradation including benA-xylX and dmpB/xylE were detected. The functional genes of nitrogen metabolism were involved in complete nitrification, traditional denitrification, assimilation nitrate reduction and dissimilation nitrate reduction. The functional contribution analysis and network analysis showed that the cooperation and competition of Thauera, Delftia, Diaphorobacter, Micavibrio and Azoarcus ensured the effective removal of aniline and nitrogen.

Growing Picochlorum oklahomensis in Hydraulic Fracturing Wastewater Supplemented with Animal Wastewater

Hydraulic fracturing is used to enhance oil and gas extraction from tight shale formations and generates millions of gallons of wastewater which needs to be cleaned up prior to disposal or reuse. The current technologies used for the management of this wastewater present technical, economic, and environmental challenges. Hence, the main objective of this study was to examine the potential of algal remediation of hydraulic fracturing wastewater (PW) as an alternative method. Considering that PW contains very low concentration of the nutrients needed for algae growth PW supplemented with animal wastewater (AW-PW) was also examined. Biomass production capacity, average biomass productivity, and specific growth rate of the microalgae strain used in the study, Picochlorum oklahomensis, were 1.87 g L−1, 268 mg L−1 day−1, and 0.35 day−1, respectively, when grown in PW. Complete nitrate, ammonia, and phosphate removal could be achieved by growing algae in PW. Supplementation of PW with animal wastewater enhanced biomass production (1.87–2.40 g L−1) and lipid content (15–25% wt) in the produced algal biomass. A mathematical model with a correlation coefficient of greater than 0.94 was developed to describe the growth kinetics of algae grown in AW-PW.

Characteristics and metabolic pathway of the bacteria for heterotrophic nitrification and aerobic denitrification in aquatic ecosystems

The present study investigated the nitrogen removal characteristics and metabolic pathway of bacteria in aquatic ecosystem, with a focus on heterotrophic nitrification and aerobic denitrification. The bacteria demonstrated significant heterotrophic nitrification and aerobic denitrification capacity. The highest ammonium-N, nitrate-N, and nitrite-N removal efficiencies were 95.31 ± 0.11%, 98.91 ± 0.05%, and 98.79 ± 0.09%, respectively. The Monod model was used to estimate the maximum rate of substrate utilization (Rmo) and the half-saturation concentration (Ks) for the two substrates, i.e., ammonium and nitrate. The kinetic coefficients were 3.34 mg/L/d (Rmo) and 30.59 mg/L (Ks) for ammonium-N, respectively, and 14.23 mg/L/d (Rmo) and 215.24 mg/L (Ks) for nitrate-N, respectively. The effects of initial nitrogen (ammonium-N or nitrate-N) concentration, temperature, and dissolved oxygen (DO) on nitrogen removal rate were investigated using response surface methodology (RSM), and the optimal conditions for nitrogen removal were determined. The principal nitrogen removal pathway of the bacteria was proposed as complete heterotrophic nitrification and aerobic denitrification, which was performed by six key genera: Arthrobacter, Pseudomonas, Rhodococcus, Bacillus, Massilia, and Rhizobium. Chryseobacterium and other denitrifying species may also reduce nitrification products (NOX−) via aerobic denitrification.

Analyzing the effect of organic carbon on partial nitrification-anammox process based on metagenomics and quorum sensing.

The effects of adding organic carbon on the performance of different partial nitrification-anammox (PNA) process (the activated sludge process and biofilm process) were studied, especially nitrogen removal, functional microbial activity, and microbial community structure. The potential influences of quorum sensing (QS) on the nitrogen metabolism were also analyzed. The results showed that the addition of organic carbon in biofilm systems could reduce total nitrogen (TN) removal percentages, while in activated systems it could increase TN removal percentages. The TN removal percentages in SBBR-CN (the biofilm system with addition of organic carbon) and SBR-CN (the activated sludge system with addition of organic carbon) were 15% and 45%, respectively, and those in SBBR-N (the biofilm system without addition of organic carbon) and SBR-N (the activated sludge system without addition of organic carbon) were 75% and 21%, respectively. Batch experiments have proved that organic carbon inhibited the activities of nitrite-oxidizing bacteria (NOB) and anaerobic ammonia oxidation (anammox) bacteria, and organic carbon could promote the activity of denitrifying bacteria in activated sludge systems. Compared with activated sludge systems, biofilm systems could protect the activity of anammox bacteria. The relative abundances of ammonia oxidizing bacteria (AOB) and anammox bacteria were decreased, while the relative abundances of denitrifying bacteria (Thauera) were increased with the addition of organic carbon. The biofilm systems were more conducive to the growth of anammox bacteria. Metagenomics revealed that the same bacteria might be involved in different nitrogen metabolism, and nitrogen metabolism was achieved through the complex cooperation among functional bacteria. Besides, functional bacteria involving in the nitrogen metabolism had genes related to QS, indicating that QS might affect the nitrogen metabolism by regulating the functional bacteria activity. PRACTITIONER POINTS: PNA was achieved through SBBR and complete nitrification was achieved through SBR under the low ammonia nitrogen concentration condition. The effect of organic carbon on biofilm and activated sludge PNA process was different under the low ammonia nitrogen concentration condition. QS and QQ may affect the nitrogen removal performance by regulating the expression of nitrogen metabolism-related genes.

Deep-level nutrient removal and denitrifying phosphorus removal (DPR) potential assessment in a continuous two-sludge system treating low-strength wastewater: The transition from nitration to nitritation

In a continuous two-sludge denitrifying phosphorus removal (DPR) process of anaerobic anoxic oxic - moving bed biofilm reactor (AAO - MBBR), nitritation was practicable through the combined regulation of high temperature (T: 30–32 °C), short hydraulic retention time (HRT: 8 h) and low dissolved oxygen (DO: 1.0–1.5 mg/L). The system lasted for 90 days with stable nitrite accumulation ratio (NAR > 60%), and the total inorganic nitrogen (TIN) removal was 7% higher than complete nitrification. Ammonia oxidizing bacteria ((AOB) 6.18–9.41%) responsible for nitritation showed a clear relationship with NAR, but Nitrospira (2.11% → 2.35%) gradually outcompeted Nitrobacter (1.19% → 0.31%) under higher temperature. During the transition from nitration to nitritation, the DPR potential (characterized by ΔPO43−/ΔNOx−) increased by 11.90% while the energy requirement of poly-β-hydroxyalkanoates (PHA) and glycogen (Gly) decreased by 12.58% and 14.50%, respectively, contributing to higher TIN (84.83%) and TP (97.45%) removals. DPR batch tests using different electron acceptors (NO3− .vs. NO3− + NO2−) revealed that removing 1 mg PO43− only consumed 7.12 ± 0.25 mg PHA via NO3− + NO2− (.vs. 8.50 ± 0.12 mg PHA via NO3−) and 16% carbon source was saved although the DPR capability was suppressed as NO2− concentration exceeded 15 mg/L. Based on the achievement of nitritation, the feasibility of integrated DPR - Anammox in the AAO - MBBR system for deep-level nutrient removal was discussed.

A salty start: Brackish water start-up as a microbial management strategy for nitrifying bioreactors with variable salinity

Nitrifying biofilms developed in brackish water are reported to be more robust to salinity changes than freshwater biofilms. This makes them a promising strategy for water treatment systems with variable salinity, such as recirculating aquaculture systems for Atlantic salmon. However, little is known about the time required for nitrification start-up in brackish water or the microbial community dynamics. To investigate the development of nitrifying biofilms at intermediate salinity, we compared the startup of moving bed biofilm reactors with virgin carriers in brackish- (12‰ salinity) and freshwater. After 60 days, the brackish water biofilm had half the nitrification capacity of the freshwater biofilm, with a less diverse microbial community, lower proportion of nitrifiers, and a significantly different nitrifying community composition. Nitrosomonas and Nitrosospira-like bacteria were the main ammonia oxidizers in the brackish water biofilms, whereas Nitrosomonas was dominant in freshwater biofilms. Nitrotoga was the dominant nitrite oxidizer in both treatments. Despite the lower nitrification capacity in the brackish water treatment, the low ammonia and nitrite concentration with rapidly increasing nitrate concentration indicated that complete nitrification was established in both reactors within 60 days. The results suggest that biofilms develop nitrification in brackish water in comparable time as in freshwater, and brackish start-up can be a strategy for bioreactors with varying salinity.

Design and function of a nitrogen and sediment removal system in a recirculating aquaculture system optimized for aquaponics

Aquaponic systems (APSs) are based upon the sustainable utilization of nitrogen and phosphorus from a recirculating aquaculture system (RAS) as the nutrient source for plant production. Since the proper management of nitrogen and suspended solids are important for nutrient utilization efficiency, their optimization was evaluated. The RAS integrated with filtration unit and nitrifying biofilter provided complete nitrification without solid accumulation. Under the optimal treatment condition for 16 d, the treated water was low in ammonia (0 mg-N/L) and high in nitrate (&gt; 6 mg-N/L) concentrations, which was appropriate for use in the cultivation of lettuce (Lactuca sativa). The RAS was then incorporated with hydroponics at a 5:1 fish: plant weight ratio. Moreover, the simplified APS was compared with a typical APS system that incorporated filtration unit and nitrifying biofilter. The natural growth of nitrifying microorganisms in the simplified APS could perform complete nitrification after 20 d of operation giving low ammonia and nitrite concentrations. The nutrient removal efficiency of the simplified APS resembled the typical system. During the aquaponics, the hydroponic unit in the aquaculture system was sufficient to control the nutrient concentrations within the appropriate levels for fish cultivation, i.e. nitrate (&lt; 20 mg-N/L) and phosphate (&lt; 3 mg-P/L).

Origin and stability of uranium accumulation-layers in an Alpine histosol

Uranium (U) accumulation in organic soils is a common phenomenon that can lead to high U concentration in montane wetlands. The stability of the immobilized U in natural wetlands following redox fluctuations and re-oxidation events, however, is not currently known. In this study, we investigated a saturated histosol that had accumulated up to 6000 ppm of U at 30 cm below ground level (bgl). Uranium in the waters feeding the wetland originates from the weathering of surrounding gneiss rocks, a process releasing trace amounts (<3 ppb) of soluble U into nearby streams. Redox oscillations in the first 20 cm bgl led to the accumulation of U, Ca, S in low permeability layers at 30 and 45 cm bgl. XRF measurements along the core showed that U strongly correlates with sulfur (S) and calcium (Ca), but not iron (Fe). We tested the stability of uranium in the histosol over a nine-month laboratory amendment of a large core of the histosol (∅ 30 cm; length 55 cm) with up to 500 ppm nitrate. Nitrate addition was followed by complete nitrate reduction and re-generation of oxidizing Eh conditions in the top 25 cm of the soil without U release to the soil pore waters above background levels (1–2 ppb). Our results demonstrate that, fast reduction of nitrate, sulfate, and Fe(III) occur in the soil without U release. The remarkable stability of sorbed U in the histosol may result from buffering by sulfide and Sn° and/or strong U(IV)-OM or U(VI)-OM enhanced by organic S moieties or bridging complexation by Ca. That U in the soil was immobile under nitrate addition for up to 9 months can inform remediation strategies based on the use of artificial wetlands to limit U mobility in contaminated sites.